Far Side was volcanically active until 2.5 billion years ago

"The volcanic activity in the lunar maria on the farside was previously believed to have ended more than 3 billion years ago, but Kaguya has confirmed that magma eruption actually continued until 2.5 billion years ago. Details of the volcanic history of the lunar farside are just beginning to emerge."

"The age of a lunar region is determined using a method called crater counting: the greater the number and density of craters, the older we assume the region to be. Using its onboard Terrain Camera, which has 10-meter resolution to observe the degtail of the lunar surface, Kaguya was able to detect craters as small as 200 to 300 meters in diameter."